1880.] 



MICROSCOPICAL JOURNAL. 



in 



above described quality had been 

 sacrificed to the attainment of 

 superior definition, and which he 

 called "defining objectives,"as dis- 

 tinguished from the others called 

 " penetrating " objectives. 



Com])aring the effects of these 

 two qualities of an objective, the 

 writer argued that the mind was 

 more likely to obtain a correct idea 

 of the stnicture of an unknown ob- 

 ject, if the images of it presented 

 to the eye by an objective, resem- 

 bled in character those received 

 by the eye direct from natural ob- 

 jects, as he claimed was the 

 case with penetrating objectives, 

 than if the mind were compelled to 

 successively compare with each 

 other, the images of separate parts 

 and different planes, and laboriously 

 trace out their relations to each 

 other. 



Referring to the ol^jection that 

 penetration was permissible in low- 

 power objectives, he said that pene- 

 tration was equally as necessary in 

 high-power objectives as in the 

 others, and referred to certain state- 

 ments of the Rev. Mr. Dallinger, 

 concerning a^^^-inch objective, made 

 for him by Powell & Lealand, and 

 which he used in his researches 

 upon septic organisms, published in 

 August, 18Y8. These statements, 

 the writer claimed, supported the 

 position taken by himself. He quo- 

 ted Mr. Dallinger's description of 

 the penetrating power and fine de- 

 finition of the ^-inch lens, as evi- 

 dence that a superior objective for 

 delicate, original work, required pen- 

 etration as well as definition. The 

 practical conclusion, he said, was, 

 that neither penetrating objectives 

 nor defining objectives were alone 

 suflicient for all classes of micros- 

 copical investigation ; but that both 

 kinds were needed, of all the pow- 

 ers, and if the microscopist was 

 limited in the number of his lenses, 



he would find the widest capabil- 

 ities in the low-power defining and 

 high-power penetrating objectives, 

 closing with the recommendation 

 that opticians should endeavor to 

 secure the best possible combination 

 of defining power with penetra- 

 tion in the same objective. 



The Sulb-section of Microscopy 

 at Boston. 



We have not deemed it advisable 

 to take up much space with a de- 

 tailed account of the proceedings of 

 the Microscopical Sub-section oi the 

 A. A. A. S., but shall confine our- 

 selves to a brief account of the stands 

 and apparatus exhibited, and to the 

 printing of a number of the articles 

 that were read. Some of these, 

 however, will have to lie over for 

 our next number. 



On Saturday, August 28th, the 

 following communications were 

 read before the Microscopical Sub- 

 section : — 



" On the Limits of Yisibility with 

 the Microscope," by A. E. Dol- 

 bear ; " Minute Anatomy of the 

 Human Larynx," by Carl Seller, 

 and " Some of the Infusoria Found 

 in Fresh Pond, Cambridge," by S. P. 

 Sharpies. Of these. Professor Dol- 

 bear's work is of general interest, 

 although it embodies nothing new. 

 The same subject has been examined 

 by Mr. Sorby, and by othere, and 

 any further discussion of the visi- 

 bility of ultimate molecules seems 

 useless, at the present day. Mr. 

 Dolbear spoke substantially as fol- 

 lows : Some years ago, it was thought 

 that the limits of visibility with the 

 microscope would be reached when 

 the object to be magnified was about 

 half a wave-length of blue or violet 

 light in dimensions, say the one- 

 hundred-thonsandth of an inch ; but 

 Robert's lines are now said to be 

 seen like pickets in a fence, and 



